Methods for forming narrow vertical pillars and integrated circuit devices having the same

ABSTRACT

In some embodiments, an integrated circuit includes narrow, vertically-extending pillars that fill openings formed in the integrated circuit. In some embodiments, the openings can contain phase change material to form a phase change memory cell. The openings occupied by the pillars can be defined using crossing lines of sacrificial material, e.g., spacers, that are formed on different vertical levels. The lines of material can be formed by deposition processes that allow the formation of very thin lines. Exposed material at the intersection of the lines is selectively removed to form the openings, which have dimensions determined by the widths of the lines. The openings can be filled, for example, with phase change material.

TECHNICAL FIELD

This invention relates generally to integrated circuit fabrication and,more particularly, to processes for forming thin vertical pillars and tothe resultant integrated circuit devices, which may include phase changememory cells.

BACKGROUND

As a consequence of many factors, including demand for increasedportability, computing power, memory capacity and energy efficiency, thedensity of electrical features in integrated circuits is continuouslyincreasing. To facilitate this scaling, the sizes of these electricalfeatures are constantly being decreased.

The trend of decreasing feature size is evident, for example, in memorycircuits or devices such as read only memory (ROM), random access memory(RAM), flash memory, resistive memory, etc. Examples of resistivememories include phase change memory, programmable conductor memory, andresistive random access memory (RRAM). To take one example, resistivememory devices may include arrays of cells organized in a cross pointarchitecture. In this architecture, the memory cells may include a cellstack having a storage element, e.g., a phase change element, in serieswith a select device, e.g., a switching element such as an ovonicthreshold switch (OTS) or diode, between a pair of conductive lines,e.g., between an access line and a data/sense line. The memory cells arelocated at the intersections of a word line and bit line and may be“selected” via application of appropriate voltages to those lines.Decreasing the sizes of the memory cells may increase cell densityand/or memory device performance.

Accordingly, there is a continuing need for methods for providingintegrated circuit features having small sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the Detailed Description ofthe Preferred Embodiments and from the appended drawings, which aremeant to illustrate and not to limit embodiments of the invention. Itwill be appreciated that the drawings are not necessarily to scale, norare features in the same drawing necessarily on the same scale as otherfeatures.

FIG. 1 shows schematic, cross-sectional side and top-down views of apartially fabricated integrated circuit.

FIG. 2 shows schematic, cross-sectional side and top-down views of thepartially fabricated integrated circuit of FIG. 1 after forming mandrelson a first level and forming spacers along sidewalls of the mandrels.

FIG. 3 shows schematic, cross-sectional side and top-down views of thepartially fabricated integrated circuit of FIG. 2 after filling gaps atsides of the spacers.

FIG. 4 shows schematic, cross-sectional side and top-down views of thepartially fabricated integrated circuit of FIG. 3 after recessingspacers to form an open spacer volume and forming, e.g., depositing, amaterial in the open spacer volume.

FIG. 5 shows schematic, cross-sectional side and top-down views of thepartially fabricated integrated circuit of FIG. 4 after forming mandrelson a second level and forming spacers along sidewalls of the mandrels.

FIG. 6 shows schematic, cross-sectional side and top-down views of thepartially fabricated integrated circuit of FIG. 5 after filling gaps atsides of the spacers on the second level.

FIG. 7 shows schematic, cross-sectional side and top-down views of thepartially fabricated integrated circuit of FIG. 6 after removing thespacers on the second level thereby forming an open spacer volume on thesecond level and also removing exposed material in the spacer volume onthe first level.

FIG. 8 shows schematic, cross-sectional side and top-down views of thepartially fabricated integrated circuit of FIG. 7 after forming, e.g.,depositing, material in the open volume on the second level.

FIG. 9 shows schematic, cross-sectional side and top-down views of thepartially fabricated integrated circuit of FIG. 8 after definingfree-standing stacks.

FIG. 10 shows a schematic, perspective view of a memory cell.

FIG. 11 shows a cross-sectional top-down view the memory cell of FIG.10.

DETAILED DESCRIPTION

Embodiments disclosed herein have application to and encompass varioustypes of integrated circuits and related apparatus. For example, whilenot limited to memory devices, some embodiments may be applied to memorydevices, including resistive memories, such as phase change memory. Itwill be appreciated that phase change memory (PCM) exploits the abilityof some materials to assume two or more stable resistance states. Forexample, memory cells may be formed with phase change materials that mayassume stable crystalline and amorphous states, which have differentelectrical resistivities. In some cases, the crystalline state can havea lower resistivity than the amorphous state. The difference inresistivity can be used to store information; for example, the differentresistance states may be used to represent different binary states(e.g., “1” states or “0” states). In some configurations, a phase changememory cell may be stably placed in more than two states, with eachstate having a different resistitivity, thereby allowing the cell tostore more information than a binary state cell.

The state of the phase change memory in a memory cell may be changed byapplication of an electrical signal to the cell. Without being limitedby theory, phase change materials are understood to change state by theapplication of heat, with different levels of heat causing transitionsto different states. Thus, the electrical signal can provide energy to aheating element proximate the phase change material (e.g., a resistiveheating wire adjacent the phase change material), thereby causing theheating device to generate heat, which causes the phase change materialto change state. It will be appreciated that the quantity of heat thatis desired determines the amount of energy supplied to the heater, andthat quantity of heat is at least partly determined by the amount ofphase change material present in a phase change memory cell.

In some embodiments, an integrated circuit may be formed having narrow,vertically-extending openings filled with material, such as phase changematerial and/or a heating element. To form these openings, crossinglines of sacrificial material, e.g., spacers, are formed on differentvertical levels. The lines on a level may be substantially parallel,while the lines on different levels cross one another. The lines ofmaterial can be formed by deposition processes that allow the formationof very thin pillars, e.g., pillars with widths less than the minimumresolution of photolithography processes used to define other featuresin the integrated circuit. Material at the intersection of the lines isselectively removed to form openings, which have dimensions determinedby the widths of the lines and, thus, can have dimensions less than thatformed by photolithography. The openings can be filled with material toform a pillar of the material. For example, phase change material and/ora conductive material for forming a heating element can be deposited inthe openings. Electrodes can be provided above and below the opening toallow electrical connection to other circuitry (e.g., bit lines and wordlines).

As described herein, various embodiments allow the formation of openingsor pillars, which may be exceptionally narrow and uniform. Theseopenings or pillars can provide benefits in various applications. Forexample, they can allow the formation of integrated circuits withexceptionally small features. In some embodiments, the amount of phasechange material in a memory cell may be reduced relative to forming thecell with processes such as photolithography. Reducing the amount ofphase change material present may decrease the sizes of the memory cell,and the smaller amount of material to be heated may decrease the powerrequirements of the heater for the memory cell. This can lower overallheat levels in a memory device containing arrays of memory cells,improving reliability and reducing the possibility that heating aparticular memory cell may disturb the state of neighboring memorycells. In addition, the ancillary electrical connections and devicesused to supply power to the heater can be made smaller and/or denser,and/or allowed to supply lower power levels, which may furtherfacilitate device scaling and/or increase device reliability.

Reference will now be made to the Figures in which like numbers refer tolike parts throughout.

FIGS. 1-9 illustrate a process flow for forming an integrated circuitwith pillars, according to some embodiments. For all of FIGS. 1-9, thecenter illustration is a cross-sectional top-down view, the left-mostillustration is a view of a cross-section taken along the Y-axis shownin the top-down view, and the right-most illustration is a cross-sectiontaken along the X-axis shown in the top-down view.

With reference to FIG. 1, schematic, cross-sectional side and top-downviews of a partially fabricated integrated circuit are shown. Thepartially fabricated integrated circuit includes a substrate 100, whichmay have various constituent features. For example, the substrate 100may include a vertically extending structure 110, which may be formed ofconductive material and may be an electrode in some embodiments.Examples of conductive materials include metals, e.g., tungsten, andmetal silicides, e.g., a cobalt silicide such as CoSi₂. Other electrodesmay be formed above the electrode 110 and, consequently, the electrode110 may be referred to as a lower electrode. The electrode 110 may besurrounded by dielectric material 120. The electrode 110 and dielectricmaterial 120 may be disposed over various other structures (not shown),including, for example, underlying conductive interconnects. Theillustrated substrate 100 may be part of a semiconductor wafer.

With reference to FIG. 2, schematic, cross-sectional side and top-downviews are shown of the partially fabricated integrated circuit of FIG. 1after forming mandrels on a first level and forming spacers alongsidewalls of the mandrels. It will be appreciated that mandrels 130 mayserve as placeholders to set the position of spacers 140. While aplurality of mandrels 130 may be provided across the substrate 100, asingle mandrel 130 is shown for ease of illustration and discussion.Mandrel 130 may be formed by forming, e.g., depositing, a layer ofmandrel material over the substrate 100 and patterning that layer ofmandrel material. The layer of mandrel material may be patterned byvarious methods, including photolithography. For example, a photoresistlayer may be deposited over the layer of mandrel material, a pattern maybe formed in the photoresist layer by photolithography, and that patternmay subsequently be transferred to the layer of mandrel material to formthe illustrated mandrel 130.

It will be appreciated that the mandrel 130 may be part of the finalintegrated circuit structure and, as a result, the material forming themandrels 130 may be chosen by considering the properties desired for themandrel 130 in that final structure. For example, the mandrel 130 may bea dielectric material to provide electrical isolation of later-formedfeatures. Examples of dielectric materials include oxides or nitrides,for example silicon oxide or silicon nitride. In some embodiments, thedielectric material is a silicon oxide.

With continued reference to FIG. 2, spacers 140 having a width t1 may beformed along sidewalls of the mandrels 130. In some embodiments, thespacers 140 may be formed by blanket depositing a layer of spacermaterial over the mandrels 130 and substrate 100. The layer of spacermaterial may be deposited by various deposition processes, includingvapor deposition processes, such as chemical vapor deposition (CVD) andatomic layer deposition (ALD). The spacer layer may be etched using adirectional etch, thereby preferentially removing horizontally extendingexpanses of material to leave spacers 140 at the sides (e.g, contacting)the mandrel 130. Consequently, in some embodiments, the thickness of thespacer layer determines the width t1 of the spacers 140, with thethickness of the layer being substantially equal to the width t1. Insome embodiments, the spacer 140 may function as electrode contacts inthe final integrated circuit structure. In some other embodiments, thespacer 140 may be formed of a material that allows it to function as aswitch, e.g., an ovonic threshold switch (OTS), in the final integratedcircuit structure. Examples of materials for forming the spacers 140 toprovide OTS functionality include compounds formed of the followingcombinations of elements: As—Te—I, TiAsSe₂, TiAsTe₂, Si—Te—As—Ge,Si—Te—As—Ge—P, Al—As—Te—Al—Ge—As—Te, Te₃₉As₃₆Si₁₇Ge₇P,As₄₀Te_((60-x))In_(x) (where 5<x<16.5), As₃₅Te_((65-x))In_(x) (where12.5<x<21.5), As₃₀Te_((70-x)) (where 12.5<x<21.5), andGe₂₀Te_((80-x))Pb_(x) (where 2<x<8).

As noted herein, in some embodiments, ALD may be used to depositexceptionally thin and uniform layers of spacer material, therebyforming exceptionally narrow spacers. In some embodiments, the spacers140 can have a width t1 of about 40 nm or less, about 25 nm or less,about 10 nm or less, or about 5 nm or less. In some embodiments, thewidth t1 may be about 2 nm or less. In some embodiments, the spacerlayer can have low non-uniformity. For example, the thicknessnon-uniformity may be about 5% or less, about 2%, about 1% or less, orabout 0.5% or less. Examples of spacer materials include Al₂O₃, HfO₂,ZrO₂, Ta₂O₅, La₂O₃, TiO₂, V₂O₅, TiN, ZrN, CrN, TiAlN, AlTiN, Ru, Pd, Jr,Pt, Rh, Co, Cu, Fe, and Ni.

With reference to FIG. 3, cross-sectional side and top-down views areshown of the partially fabricated integrated circuit of FIG. 2 afterfilling gaps 150 at sides of the spacers 140. It will be appreciatedthat the features in the cross-sectional views shown in FIG. 3 and inthe other figures may be repeated across the substrate 100, such thatgaps 150 are defined between the spacers 140 and a neighboring spacerand mandrel (not shown). In some embodiments, the gaps 150 may be filledby forming, e.g., depositing, filler material 160 into the gaps 150. Thedeposited filler material 160 may overfill the gaps 150, and then beplanarized. In some embodiments, planarization may include removingmaterial forming peaks on the upper surface of the partially fabricatedintegrated circuit, e.g., by performing a chemical mechanical polishing(CMP) process to remove excess filler material 160 and/or other materialon the upper surface.

The volume occupied by the spacers 140 between the filler material 160and the mandrels 130 may be referred to as a spacer volume. The spacers140 may then be selectively recessed to form an opening, e.g. a trench,in the spacer volume, thereby providing a spacer volume that ispartially open.

With reference to FIG. 4, schematic, cross-sectional side and top-downviews are shown of the partially fabricated integrated circuit of FIG. 3after recessing spacers 140 to form an open spacer volume and forming,e.g., depositing, a material 170 in the open spacer volume. It will beappreciated that the open spacer volume may be filled with the material170, e.g., a dielectric material, which may then be planarized, e.g., byCMP. Examples of dielectric materials include oxides and nitrides, suchas silicon oxide or silicon nitride. In some embodiments, the dielectricmaterial is a silicon nitride.

With reference to FIG. 5, schematic, cross-sectional side and top-downviews are shown of the partially fabricated integrated circuit of FIG. 4after forming mandrels 230 on a second level and forming spacers 240along sidewalls of the mandrels 230. The spacers 240 have a width t2.The mandrels 230 and spacers 240 may be formed by processes and usingmaterials such as those discussed herein with respect to mandrels 130and spacers 140 (FIG. 2), respectively. For example, the spacers 240 maybe formed by blanket depositing a layer of spacer material and thendirectionally etching that layer to form the spacers 240. The thicknessof the layer of spacer material may determine the width t2. In someembodiments, the width t2 may be about 40 nm or less, about 25 nm orless, about 10 nm or less, or about 5 nm or less. As seen in the centertop-down view, the spacers 240 may extend along an axis crossing theaxis along which the spacers 140 extend and the points of intersectionof the crossing axes may be vertically aligned with the underlyingelectrodes 110. As illustrated, in some embodiments, as seen in atop-down view, the spacers 240 may extend substantially perpendicular tothe spacers 140. The spacers 240 may be formed directly over and incontact with the underlying material 170.

After forming the spacers 240, gaps 250 may be present at their sides.It will be appreciated that the features in the cross-sectional viewsshown in FIG. 5 may be repeated across the substrate 100, such that thegaps 250 are defined between the spacers 240 and a neighboring spacerand mandrel (not shown). In some embodiments, the gaps 250 may be filledby forming, e.g., depositing, filler material 260, which may overfillthe gaps 250, and then planarizing the upper surface of the resultingstructure. In some embodiments, planarization may include removingmaterial forming peaks on the upper surface, e.g., by performing achemical mechanical polishing (CMP) process to remove excess fillermaterial and/or other material on the upper surface. FIG. 6 showsschematic, cross-sectional side and top-down views of the partiallyfabricated integrated circuit of FIG. 5 after filling gaps at sides ofthe spacers on the second level and planarizing the exposed uppersurface.

The spacers 240 may subsequently be selectively removed to form trenchesin the volume formerly occupied by the spacers 240 between the mandrels230 and filler 260. The trenches expose portions of the underlyingmaterial 170 (FIG. 4) filling the spacer volume in the first level. Thisexposed material 170 may be selectively removed. FIG. 7 shows schematic,cross-sectional side and top-down views of the partially fabricatedintegrated circuit of FIG. 6 after removing the spacers 240 on thesecond level and removing exposed material 170 in the spacer volume onthe first level, thereby forming an opening 262 (e.g., trench) on thesecond level, which extends downwards to form an open volume on thefirst level. That open volume may then be filled with material and thecorresponding filled volume may be referred to as the volume 264, whichmay take the form of a vertically elongated volume or channel. Thespacers 240 (FIG. 6) and exposed material 170 may be removed by exposureto one or more etches. In some embodiments, a wet etch may be used toselectively remove the spacers 240 and a directional etch may be used toselectively remove exposed material 170. In some other embodiments, asingle directional etch may be used to remove the spacers 240 andexposed material 170, depending upon whether the single directional etchprovides sufficient selectivity for etching both those features. Asshown in FIG. 7's top-down view, the narrow volume 264 may be defined atthe intersection of the spacers 240 (FIG. 6) and exposed material 170.

In some embodiments, the etch processes use to form the volume 264 canprovide a volume with more uniform sidewalls than those formed byphotolithography. For example, the edge roughness of the sidewalls maybe less than 3 nm, less than about 2 nm, or less than about 1 nm.

FIG. 8 shows schematic, cross-sectional side and top-down views of thepartially fabricated integrated circuit of FIG. 7 after forming, e.g.,depositing, material 270 in the open volume 262 (FIG. 7) on the secondlevel. As illustrated, the material 270 may also extend into the narrowvolume 264 (FIG. 7) on the first level. In some embodiments, thematerial 270 may be a material which provides a desired electricalfunctionality in the narrow volume 264. In some embodiments, thematerial 270 is a material that may exist stably in one or more states.For example, the material 270 may be a phase change material. Examplesof phase change materials include chalcogenide materials, such as thoseformed from germanium (Ge), antimony (Sb), and tellurium (Te), andvarious combinations thereof. Examples of materials include binarycompounds with one or more of these elements (e.g., GeTe, Ge—Sb, In—Se,Sb—Te, Ge—Sb, Ga—Sb, In—Sb, As—Te, and Al—Te); ternary compounds withone or more of these elements (e.g., Ge—Sb—Te, Te—Ge—As, In—Sb—Te,Te—Sn—Se, Ge—Se—Ga, Bi—Se—Sb, Ga—Se—Te, Sn—Sb—Te, and In—Sb—Ge); andquaternary compounds with one or more of these elements (e.g.,Te—Ge—Sb—S, Te—Ge—Sn—O, Te—Ge—Sn—Au, Pd—Te—Ge—Sn, In—Se—Ti—Co,Ge—Sb—Te—Pd, Ge—Sb—Te—Co, Sb—Te—Bi—Se, Ag—In—Sb—Te, Ge—Sb—Se—Te,Ge—Sn—Sb—Te, Ge—Te—Sn—Ni, Ge—Te—Sn—Pd, and Ge—Te—Sn—Pt). It will beappreciated that the ratios of the various elements are not listed inthe examples above and may be varied to achieve phase change behaviorwith multiple stable states. An example of a phase change material isGe₂Sb₂Te₅. In some embodiments, the phase change material 270 isdeposited such that it overflows the volume 264 and excess material maybe removed, e.g., by CMP, so that it stays substantially completelywithin the volume 264.

With reference to FIG. 9, an upper electrode 280 may be formed on athird level over the material 270 and the resulting structure may bemasked to define free-standing, spaced-apart stacks 290; FIG. 9 showsschematic, cross-sectional side and top-down views of the partiallyfabricated integrated circuit of FIG. 8 after defining the free-standingstacks 290. The upper electrode 280 may be formed by blanket depositinga layer of conductive material. A mask may then be formed over theresulting structure and the mask may be patterned (e.g., byphotolithography) to form a pattern corresponding the free-standingstacks 290. The layers of material that make up the free-standing stacks290 are subsequently subjected to one or more directional etchesselective for those materials, thereby defining the free-standing stacks290. As illustrated, the conductive material 270 and 140 take the formof plates after the free-standing stacks 290 are formed. As alsoillustrated, these plates may be elongated along crossing axes.

In some embodiments, a dielectric material may be deposited between thestacks 290 to electrically isolate those stacks from one another. Insome embodiments, the dielectric material between the stacks 290 is thesame material as the dielectric material 170. In some other embodiments,the dielectric material between the stacks 290 is different from thedielectric material 170.

It will be appreciated that each of the free-standing stacks 290 mayconstitute a memory cell 290. FIG. 10 shows a schematic, perspectiveview of the memory cell 290. The memory cell 290 may be a phase changememory cell in which the material 270 is a phase change material. One ofthe top or bottom electrodes 280, 110 may provide current to the cell290, while the other electrode 280, 110 provides a drain. The phasechange material 270 and spacer 140 on the second and first levels,respectively, provide electrical contacts to the top and bottomelectrodes 280, 110, respectively. Current passing through the material270 in the relatively small volume 264 can cause resistive or jouleheating, which may heat and change the state of portion 270 a of thephase change material 270 in the narrow volume 264. As noted herein, thestate may be selected based upon the amount of energy (and resultingheat) applied to the material in the volume 264. It will be appreciatedthat, in some embodiments, other materials, e.g., adhesion layers, maybe disposed between various materials in the stack 290, e.g., betweenthe phase change material 270 and the top electrode 280.

In some other embodiments, a separate heater may be used to heat thephase change material 270. For example, the spacers 140 may be formed ofa material with electrical resistivity sufficient to heat and to changethe state of the phase change material 270. Examples of materials forsuch a heater include W, Ni, Pt, TiN, TiW, TaN, TaSiN, TiSiN, and NbN.These materials may be originally-deposited during formation of thespacers 140, or may be deposited into the spacer volume after removingthe originally-formed spacers.

FIG. 11 shows a cross-sectional top-down view the memory cell of FIG.10. As noted herein, the narrow volume 264 is defined at theintersection of the spacers 140 and 240, which each define a spacervolume into which other materials 170, 270 may be deposited. Thus, thoseother materials may then serve to set the dimensions of the openings264. For example, as illustrated in FIG. 11, the widths of the narrowvolume 264 are defined by the intersection of the material 170 (e.g., adielectric material) filling the spacer volume on the first level, andthe material 270 (e.g., a phase change material) filling the spacervolume on the second level. Consequently, the cross-sectional dimensionsof the volume 264 may be equal to the widths t1 and t2 of the spacervolumes on the first and second levels, respectively. Thus, the volume264 and the material within it may extend substantially the entire widthof the spacer volumes. For example, the volume 264 may extend the entirewidth of the laterally elongated region formed by the dielectricmaterial 170. In some embodiments, as seen in a top-down view, theresulting volume 264 may substantially be in the shape of aparallelogram, including, for example, a rhomboid shape, examples ofwhich include a rectangular or square shape. It will be appreciated thatthe corners of the shape may be rounded, e.g., because etches used inpattern formation may form rounded corners, while the generalorientation of the sidewalls to one another may correspond substantiallyto the shape of a parallelogram and thus be said to be substantially tothe shape of a parallelogram.

The memory cell 290 may form part of various devices utilizing memory.For example, the memory cell 290 may be used in personal computers,portable memory sticks, solid state drives (SSDs), digital cameras,cellular telephones, portable music players, movie players, and otherelectronic devices.

It will be appreciated that various processes and/or structuresdescribed herein may be omitted, repeated, combined with other processesor other altered. In some embodiments, one or both of the electricalcontacts 140, 270 (FIG. 10) may be omitted. This may be accomplished,for example, by removing all material above the level of the volume 264after filling that volume. For example, phase change material 270 andother material above the top of the volume 264 may be removed by CMPafter forming the structure of FIG. 8. The lower electrical contact 140may be omitted by completely removing the spacer 140 after forming thestructure of FIG. 3.

In some other embodiments, the processing involved with forming theparticular structures of FIG. 4 may be omitted. For example, afterforming the structure of FIG. 3, spacers 240 (FIG. 5) may be formeddirectly over that illustrated structure and the volume 264 may beformed by removing the spacer 240 and the part of the spacer 140 exposedby the removal of the spacer 240. Material (e.g., phase change material)may then be deposited into the resulting open volume.

It will be appreciated that where conductive material fills the narrowopenings 264, the filler in the opening may be referred to as aconductive line or wire. While discussed with reference to phase changememories and materials, the openings 264 may be filled with othermaterials. For example, other conductive materials may fill the openings264 to form electrical fuses, resistive switching memory (e.g., RRAM),or other structures benefitting from thin wire structures.

It will be understood that the invention can take the form of variousembodiments, some of which are discussed above and below.

In some embodiments, a method of forming an integrated circuit includesforming a first level mandrel on a first level over a substrate. A firstset of spacers is formed along sidewalls of the first level mandrel. Afirst level filler material is deposited at sides of spacers of thefirst set of spacers, the first level filler material and the firstlevel mandrels defining a first level spacer volume therebetween. Asecond level mandrel on a second level is formed above the first levelmandrel and the first level spacer volume, the second level mandrelcrossing a width of the first level mandrel. A second set of spacers isformed along sidewalls of the second level mandrel. A second levelfiller material is deposited at sides of spacers of the second set ofspacers. The second set of spacers is selectively removed to exposeportions of the first level spacer volume. The exposed material in thefirst level spacer volume is selectively removed to form openings on thefirst level. The openings are filled and an upper electrode is formed ona third level over the second level, the upper electrode extendingdirectly over one or more of the filled openings on the first level.

In some embodiments, filling the opening comprises forming a phasechange material in the opening. Selectively removing the second set ofspacers may define trenches between the second level mandrels and thesecond level filler material, wherein filling the openings also fillsthe trenches with phase change material. The method may further compriseremoving the phase change material outside of the openings beforeforming the top electrode. The top electrode may electrically contactthe phase change material filling the trenches and phase change materialforms a part of a phase change memory cell. The method may furthercomprise providing a bottom electrode underlying the first set ofspacers, wherein the first set of spacers are formed of a conductor andelectrically interconnect the phase change material in the openings tothe bottom electrodes.

In some embodiments, the method may further comprise recessing spacersof the first set of spacers after forming the first level fillermaterial and before forming the second level mandrel, thereby definingtrenches in the first level spacer volume; and forming a dielectricmaterial in the trenches, wherein selectively removing the exposedmaterial removes portions of the dielectric material.

In some embodiments, forming the first set or second set of spacerscomprises: blanket depositing a layer of spacer material on the first orthe second level mandrel; and subjecting the layer of spacer material toa directional etch to define the first or second set of spacers.

In some other embodiments, a method for forming an integrated circuitincludes providing a first set of spaced-apart lines of sacrificialmaterial separated by dielectric material. A second set of spaced-apartlines of sacrificial material separated by dielectric material isprovided, the second set of spaced-apart lines crossing and contactingtops of lines of the first set of spaced apart lines. The second set ofspaced-apart lines and the portions of the first set of spaced-apartlines at the intersection of the first and second sets of spaced apartlines are selectively removed. An electrode is formed over a remainderof the first set of spaced apart lines.

In some embodiments, the integrated circuit is a phase change memory andselectively removing the second set of spaced-apart lines and theportions of the first set of spaced-apart lines may define openings atthe intersection of the first and second sets of spaced apart lines, andthe method further comprises: filling the openings with a phase changematerial. The method may further comprise, after filling the openings,etching material around the opening to define free-standing memory cellstacks separated by open space, wherein each stack comprises an openingfilled with the phase change material. The method may further comprise,depositing dielectric material in the space separating the stacks. Thedielectric material in the space separating the stacks may be differentfrom dielectric material separating the first set of spaced-apart linesof sacrificial material.

In yet other embodiments, an integrated circuit includes a memory cell.The memory cell includes a bottom electrode; an upper electrode; and aconductive line in a channel extending vertically between the bottom andupper electrodes. The conductive line has a cross-section substantiallyin the shape of a parallelogram as seen in a top down view. Each side ofthe parallelogram may have a length of about 40 nm or less.

In some embodiments, a width of the conductive line, as seen from a topdown view, is defined by a width of a spacer volume. The length may beabout 25 nm or less in some embodiments. The line edge roughness may beabout 3 nm or less. In some embodiments, the integrated circuit mayfurther comprise a phase change material disposed in the channel andextending between the conductive line and the upper electrode. Theconductive line may comprise a resistive heater. The resistive heatermay include a material chosen from the group consisting of W, Ni, Pt,TiN, TiW, TaN, and NbN. In some embodiments, the cross-section may besubstantially in the shape of a square.

In other embodiments, an integrated circuit includes a memory cell. Thememory cell has a bottom electrode; an upper electrode; and a conductivewire extending vertically between the bottom and upper electrode. Theconductive wire is disposed within a discrete, laterally elongatedinsulating region. The conductive wire extends across an entire width ofthe insulating region.

In some embodiments, a cross-section of the insulating region may have aparallelogram shape as seen in a top down view. In some embodiments, theconductive wire may be at least partly formed of phase change material.

In yet other embodiments, a memory device includes a memory cell. Thememory cell includes a lower electrode; a vertically-extending lowerconductive plate above and electrically connected to the lowerelectrode; a vertically-extending conductive wire above and electricallyconnected to the lower conductive plate; a vertically-extending upperconductive plate above and electrically connected to the wire; and anupper electrode above and electrically connected to thevertically-extending second conductive plate. The upper and lowerconductive plates are elongated into crossing directions. In someembodiments, the conductive wire may comprise a phase change material.

Accordingly, although certain embodiments are described herein, otherembodiments that are apparent to those of ordinary skill in the art,including embodiments that do not provide all of the features and/oradvantages set forth herein, are also encompassed by this invention.Accordingly, the scope of the present invention is defined only byreference to the appended claims.

What is claimed is:
 1. A method of forming an integrated circuit,comprising: forming a first level mandrel on a first level over asubstrate; forming a first set of spacers along sidewalls of the firstlevel mandrel; forming a first level filler material at sides of spacersof the first set of spacers, the first level filler material and thefirst level mandrels defining a first level spacer volume therebetween;forming a second level mandrel on a second level above the first levelmandrel and the first level spacer volume, the second level mandrelcrossing a width of the first level mandrel; forming a second set ofspacers along sidewalls of the second level mandrel; forming a secondlevel filler material at sides of spacers of the second set of spacers;selectively removing the second set of spacers to expose portions of thefirst level spacer volume; selectively removing the exposed material inthe first level spacer volume to form openings on the first level;filling the openings; and forming a top electrode on a third level overthe second level, the electrode extending directly over one or more ofthe filled openings on the first level.
 2. The method of claim 1,wherein filling the opening comprises forming a phase change material inthe opening.
 3. The method of claim 2, wherein selectively removing thesecond set of spacers defines trenches between the second level mandrelsand the second level filler material, wherein filling the openings alsofills the trenches with phase change material.
 4. The method of claim 3,further comprising removing the phase change material outside of theopenings before forming the top electrode.
 5. The method of claim 3,wherein the top electrode electrically contacts the phase changematerial filling the trenches and phase change material forms a part ofa phase change memory cell.
 6. The method of claim 2, further comprisingproviding a bottom electrode underlying the first set of spacers,wherein the first set of spacers are formed of a conductor andelectrically interconnect the phase change material in the openings tothe bottom electrodes.
 7. The method of claim 1, further comprising:recessing spacers of the first set of spacers after forming the firstlevel filler material and before forming the second level mandrel,thereby defining trenches in the first level spacer volume; and forminga dielectric material in the trenches, wherein selectively removing theexposed material removes portions of the dielectric material.
 8. Themethod of claim 1, wherein forming the first set or second set ofspacers comprises: blanket depositing a layer of spacer material on thefirst or the second level mandrel; and subjecting the layer of spacermaterial to a directional etch to define the first or second set ofspacers.
 9. A method for forming an integrated circuit, comprising:providing a first set of spaced-apart lines of sacrificial materialseparated by dielectric material; providing a second set of spaced-apartlines of sacrificial material separated by dielectric material, thesecond send of spaced-apart lines crossing and contacting tops of thefirst set of spaced apart lines; selectively removing the second set ofspaced-apart lines and portions of the first set of spaced-apart linesat the intersection of the first and second sets of spaced apart lines;and forming an electrode over a remainder of the first set of spacedapart lines.
 10. The method of claim 9, wherein the integrated circuitis a phase change memory and wherein selectively removing the second setof spaced-apart lines and the portions of the first set of spaced-apartlines defines openings at the intersection of the first and second setsof spaced apart lines, further comprising: filling the openings with aphase change material.
 11. The method of claim 10, further comprising,after filling the openings, etching material around the opening todefine free-standing memory cell stacks separated by open space, whereineach stack comprises an opening filled with the phase change material.12. The method of claim 11, further comprising depositing dielectricmaterial in the space separating the stacks.
 13. The method of claim 12,wherein the dielectric material in the space separating the stacks isdifferent from dielectric material separating the first set ofspaced-apart lines of sacrificial material.
 14. An integrated circuit,comprising: a memory cell, comprising: a bottom electrode; an upperelectrode; and a conductive line in a channel extending verticallybetween the bottom and upper electrodes, the conductive line having across-section substantially in a shape of a parallelogram as seen in atop down view, each side of the parallelogram having a length of about40 nm or less.
 15. The integrated circuit of claim 14, wherein a widthof the conductive line, as seen from a top down view, is defined by awidth of a spacer volume.
 16. The integrated circuit of claim 14,wherein the length is about 25 nm or less.
 17. The integrated circuit ofclaim 14, wherein line edge roughness is about 3 nm or less.
 18. Theintegrated circuit of claim 14, further comprising a phase changematerial disposed in the channel and extending between the conductiveline and the upper electrode.
 19. The integrated circuit of claim 18,wherein the conductive line comprises a resistive heater.
 20. Theintegrated circuit of claim 19, wherein the resistive heater includes amaterial chosen from the group consisting of W, Ni, Pt, TiN, TiW, TaN,TaSiN, TiSiN, and NbN.
 21. The integrated circuit of claim 14, whereinthe cross-section is substantially in the shape of a square.
 22. Anintegrated circuit, comprising: a memory cell, comprising: a bottomelectrode; an upper electrode; and a conductive wire extendingvertically between the bottom and upper electrodes, the conductive wiredisposed within a discrete, laterally elongated insulating region, theconductive wire extending across an entire width of the insulatingregion.
 23. The integrated circuit of claim 22, wherein a cross-sectionof the insulating region has a parallelogram shape as seen in a top downview.
 24. The integrated circuit of claim 22, wherein the conductivewire is at least partly formed of phase change material.
 25. A memorydevice, comprising: a memory cell, the memory cell comprising: a lowerelectrode; a vertically-extending lower conductive plate above andelectrically connected to the lower electrode; a vertically-extendingconductive wire above and electrically connected to the lower conductiveplate; a vertically-extending upper conductive plate above andelectrically connected to the wire; and an upper electrode above andelectrically connected to the vertically-extending upper conductiveplate, the upper and lower conductive plates elongated into crossingdirections.
 26. The memory device of claim 25, wherein the conductivewire comprises a phase change material.